1. Field of the Invention
The invention relates to a filter arrangement for separating and converting exhaust particulates from a stream of exhaust gas and its operation.
2. Description of the Prior Art
In the apparatus as known from U.S. Pat. No. 5,141,714 the exhaust particulates are separated at the pore borders of porous ceramics and incinerated from time to time by applying a voltage to the electrodes of the filter. Whereas the separation of the exhaust particulates therefore occurs substantially mechanically, the applied direct voltage is used for the thermal incineration of the deposited particulates, which is caused by the relatively high currents over the conductive exhaust particulate deposits.
In an alternative embodiment, the porous ceramics are penetrated by axially extending channels through which exhaust gas is conducted. The channels are open at one end and closed off at the other end. The state of the art provides to distribute the channels in a chessboard-like manner, which channels are open and closed at one and the same face side and are substantially square in their shape. Pressure differences thus build up over all four walls of each channel, so that the exhaust gas flows through all four walls of each channel and exhaust particulates contained therein are deposited about the pores of said walls. In the case of an application of a direct voltage for the purpose of thermal incineration of the exhaust particulate deposits, high local temperatures occur within the entire honeycomb body, which places high stresses on the filter material. Moreover, this type of exhaust particulate incineration is linked to a high input of energy.
In order to reach the temperature required for incinerating the deposited exhaust particulates, it is also known to use an additive and a subsequent injection of fuel, which is only possible by a common-rail injection system, and the arrangement of an additional catalyst.
This discontinuous regeneration is not only very complex, but may fail completely under extreme cold and thus lead to a complete failure of the diesel vehicle.
In the method as described in AT 404 285 B (EP 0 332 609 A), the exhaust particulate is separated by an electric direct voltage field following a charging in the channels which are opened on either side of a honeycomb body made of a dense ceramic material and is oxidized continuously in an electro-chemical manner by a gas plasma into carbon dioxide which is excited by the separating field. Within the scope of the geometry of the channels which are open on either side, said direct voltage field has the task on the one hand to ensure the separation of the exhaust particulates and on the other hand to ensure the incineration of the separated particulates. The latter requires the use of high direct voltages, which may lead to structural damage to the honeycomb filter, especially in cases when the undesirable formation of a spark occurs.